Update __version__ for travis deployment to testpypi

.travis.yml

before_deploy:
  - python $TRAVIS_BUILD_DIR/ci/travis_set_build.py --file-paths '("<project>", "__init__.py")' --skip "$TRAVIS_TAG"
deploy:
  - provider: pypi
    server: https://testpypi.python.org/pypi
    distributions: sdist
    user: <username>
    password:
      secure: <encrypted_password>
    skip_cleanup: true
    on:
      branch: master
      tags: false
      condition: $TRAVIS_PYTHON_VERSION = "2.7"

travis_set_build.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-
"""Update the version string with a build number."""

from __future__ import absolute_import
from __future__ import print_function

import io
import os
import re


PROJECT_ROOT = os.path.abspath(os.path.join(
    os.path.dirname(os.path.abspath(__file__)),
    os.pardir)
)
BUILD_NUMBER = os.environ.get('TRAVIS_BUILD_NUMBER', '')
BUILD_TYPE = 'dev'  # See PEP 440


def replace(file_path, pattern, repl, flags=0):
    with io.open(file_path, mode="r+", newline='') as fh_:
        file_contents = fh_.read()
        file_contents = re.sub(pattern, repl, file_contents, flags=flags)
        fh_.seek(0)
        fh_.truncate()
        fh_.write(file_contents)


def append_version(build, file_paths):
    # The version line must have the form
    # __version__ = 'ver'
    pattern = r"^(__version__ = ['\"])([^'\"]*)(['\"])"
    repl = r"\g<1>\g<2>.{0}\g<3>".format(build)
    version_file = os.path.join(PROJECT_ROOT, *file_paths)
    print(
        'Updating version in version_file "{0}" with build "{1}"'
        .format(version_file, build)
    )
    replace(version_file, pattern, repl, flags=re.M)


def main(args):
    skip = args.skip
    build = args.build
    build_type = args.build_type
    file_paths = args.file_paths

    if skip:
        print(
            'Not updating version for this build, `skip` set to "{0}"'
            .format(skip)
        )
    else:
        append_version('{0}{1}'.format(build_type, build), file_paths)


if '__main__' == __name__:
    import argparse
    parser = argparse.ArgumentParser(description=__doc__)
    parser.add_argument(
        '--skip',
        default=False,
        help=(
            'If set to any non-false value, skips updating the version. '
            '(default: {0})'.format(False)
        )
    )
    parser.add_argument(
        '--build',
        default=BUILD_NUMBER,
        help=(
            'Build number to append to the version. Will default to the env '
            'TRAVIS_BUILD_NUMBER or an empty string. (default: {0})'
            .format(BUILD_NUMBER)
        )
    )
    parser.add_argument(
        '--build-type',
        default=BUILD_TYPE,
        help=(
            'Build type to append to the version. See PEP 440. PyPi will not '
            'accept non-compliant version identifiers (default: {0})'
            .format(BUILD_TYPE)
        )
    )
    parser.add_argument(
        '--file-paths',
        required=True,
        help=(
            'Tuple of paths relative to the project root to a file containing '
            'the version string.'
        )
    )

    args = parser.parse_args()
    main(args)

Example above assumes travis_set_build.py will be in a sub-directory of the project named ci...